Small Grains Disease Update 06/08/20

I received few, if any, reports of fungal disease issues in small grains this past week.  The risk models for tan spot, Septoria, leaf rust, and Fusarium head blight too have remained relatively quiet across much of the state.  Meanwhile, the crop is rapidly advancing through its development as temperatures soared into the nineties across much of the state. 

 I expect much of the oats to have the flag leaf fully extended (Feekes 9) and reaching the boot stage.  Some of the earliest seeded oats may actually already have reached heading (Feekes 10).  Feekes 9 is the optimum time to spray a fungicide to control crown rust.  And while the spores of either leaf or stripe rust in wheat have to be blown up from Kansas, Nebraska, and South Dakota, spores of crown rust in oats do not.  

Buckthorn is the alternate host of crown rust of oats.  This is the time of year you will find pycnia on the underside of buckthorn leaves (photo courtesy of South Dakota State University). These pycnia will produce the spores that infect the oats and cause crown rust.  If you have some time, I encourage you to find some buckthorn and see whether they have these bright orange pycnia on the underside of the leaves.

I favor the use of fungicides to prevent and control crown rust in oats given that buckthorn is common across much of Minnesota and most oat varieties lack resistance to crown rust.  Given the weather forecast and the recent rains,  I expect crown rust in oats to ramp up quickly, especially in the SE part of the state.  The optimum timing for crown rust is Feekes 9.  A number of the fungicides labeled for control of crown rust can be applied up to 50% heading (Feekes 10.5).  Simply read and follow the directions on the label. 

I did receive a few reports of English grain and bird cherry-oat aphids in winter wheat at levels high enough to trigger an insecticide application. The locations across the state where these aphids have been reported suggest that we have had multiple influxes of aphids that were large enough to create treatable infestations across whole fields.  I implore you to actively scout for aphids, especially across the southern half of the state.